The demand for improved network coverage, improved capacity and increasing bandwidth for both voice and data services in wireless systems has led to development of a number of radio access technologies (RATs) including, but not limited to, Global Systems Mobile Communications (GSM), Wideband Code Division Multiple Access (WCDMA), High Speed Packet Access (HSPA) including High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), and Long Term Evolution (LTE) including support for carrier aggregation in LTE Release 10 and beyond) in the Third Generation Partnership Project (3GPP), IEEE 802.11b/a/g/n, 802.16a/e and 802.20, as well as cdma2000 1× and cdma2000 EV-DO in 3GPP2.
3GPP WCDMA Release 8 introduced support for simultaneous use of two HSDPA downlink component carriers (2C-HSDPA), improving bandwidth usage with frequency diversity and resource pooling. 3GPP Release 9 introduced support for multiple-input multiple-output (MIMO) to the multicarrier downlink WCDMA. Release 9 also introduced support for two HSUPA uplink component carriers. 3GPP Release 10 introduced support for up to 4 downlink component carriers (4C-HSDPA), and Release 11 introduced support for up to 8 downlink carriers (8C-HSDPA).
3GPP LTE Release 10 introduced support for simultaneous transmission and/or reception using radio resources of a plurality of component carriers between a network node (i.e., evolved NodeB (eNB)) and a mobile terminal, (i.e., a wireless transmit/receive unit (WTRU)) within the same transmission time interval.
One of the objectives for LTE is to allow operators to deploy LTE using the same sites as for WCDMA deployments, and thereby reducing deployment and radio planning costs. Some operators may deploy both WCDMA/HSPA and LTE in the same coverage areas, with LTE as a data enhancement overlay. LTE deployments may have similar coverage as the existing WCDMA/HSPA deployments. Multi-mode wireless transmit/receive units (WTRUs), for example, supporting both WCDMA/HSPA and LTE, would be widely used.
Release 10 HSPA with MIMO offers downlink peak data rates of 42 Mbps, while Release 10 multicarrier HSPA will further increase the peak rate by introducing support for up to four downlink carriers. LTE Release 8/9 offers up to 100 Mbps in the single carrier downlink, while LTE Release 10 with (intra-RAT) carrier aggregation will further increase the peak rate by combining transmission resources of up to 5 component carriers. Spectrum is a costly resource and not all frequency bands may be available to all operators. Operators may offer support for both HSPA and LTE services, but carrier aggregation may be limited to at most 2-3 component carriers per RAT for a given operator. In addition, legacy deployments may be maintained for a foreseeable future while LTE is being deployed. This may lead to a situation where operators may see periods of underutilization of radio resources/spectrum and capacity in one of their RATs.